The joining of electrical conductors to another element, such as a connector, in a system usually involves the use of an adhesive, and/or the use of mechanical means, such as crimping or a solder connection. All of these have some disadvantages.
Adhesives
Electrical or thermal contact between elements can sometimes be provided by means of an adhesive. For example, a joint between a high surface area element in an electrolytic capacitor may be formed by means of a complex cellulose binder and an aluminum or titanium foil. This type of binding system can generate a substantially high internal resistance that can severely degrade the performance of the capacitor. This internal resistance can also serve to increase the capacitor time constant (τ=R*C). Other binding examples can include epoxy bonding of the components involved. Such bonding may have dual functions, including (1) providing a mechanical bond, and (2) carrying heat, as seen with bonding of elements of an airplane or jet engine close to a heat source.
In the case of thermal junctions, the provision of good contact area can often be difficult. For example, it can be difficult to provide a good contact at the junction between an integrated circuit housing and a heat sink, where a thermal resistance of more than 20 degrees may be needed to drive, for instance, 150 watts per square cm though the junction.
Mechanical Means
It has been shown by the Kuhlmann-Wilsdorf theory of electrical contacts, and by analogy through the R. Holm theory for electrical contacts, that electrical current or thermal energy must necessarily pass though two contacting surfaces in only a few, or perhaps up to 50 atomic contact spots. Interestingly, this is not strongly dependent on the total area of contact, but rather can be dependent upon clamping force between contacts. This limitation of the total surface area that may be in actual contact between a connector and its corresponding contacting element can generally introduce a severe electrical or thermal contact resistance.
Solder Connections
To overcome this contact resistance and improve overall conductivity, the effective contact area may need to be increased. One means of accomplishing this is by soldering. However, the lead-tin alloys in common use for soldering, or even lead free solders (e.g., silver-antimony-tin), can have a strong tendency to form intermetallic compounds or layers at the solder joint or junction. Formation of intermetallic compounds usually occurs because, for instance, the tin-copper etc., present in the solder can exhibit fast diffusion when coupled with common conductors, such as copper, generally used for both thermal and electrical conduction. Moreover, the formation of intermetallic compounds or layers can continue to occur, over time, even at ambient temperatures. The consequence of such a formation at these junctions is that the intermetallic layer itself can become brittle (i.e., degradable), as well as electrically and thermally resistive, leading to an increasing resistance or even a catastrophic mechanical failure at solder junctions, especially when these junctions have a different coefficient of thermal expansion.
This holds true for both thermal and electrical junctions. Examples of solder system degradation due to intermetallic formations have been widely reported in the automotive industry, aerospace industry, and even in military missiles.
A common approach for addressing this problem has been the introduction of a “silver powder containing grease” between a heat generating element and a heat dissipating element. This grease can increase thermal transport, as it provides an additional thermal path, even though the grease may be of high thermal resistance itself. Fillers, such as silver powders, can often be added to this grease, and can also help in improving heat.
In addition to the above issues, there does not currently exist a design for joining and maximizing the number of conductive nanostructures involved in conductivity to the devices in the macro-world, while enhancing or maintaining the efficiency of the electrical or thermal transport exhibit by these conductive nanostructures.
In light of these issues, it would be desirable to provide a way to allow for efficient interaction between a nanoscale conductive element and the traditional electrical and/or thermal circuit system, while minimizing electrical or thermal resistance and improve overall conductivity.